Photo-electric tube



Aug. 8, 1933. A. J. MoMAsTl-:R

PHOTO ELECTRIC TUBE Filed Aug. 17, 1929 Patented Aug. 8, 1933 UNVU@ STATES pHoro-ELECTRIC TUBE Archie J. McMaster, Chicago, Ill., assignor to G-M Laboratories, nc.,.Chicag0, Ill.

Application August 17, 1929. Serial No. 386,527

2 Cairns.

My invention relates to photoelectric tubes and more particularly to photoelectric tubes of the electron emission type.

Photoelectric tubes usually consist of an eX- hausted envelope which may or may not contain an inert gas to increase the sensitivity of the tube. It is customary to coat the interior surface of the envelope with an electron emissive substance such as an alkali metal to form the lcathode of the tube. This method has certain disadvantages due to the fact that measures must be taken to insure contact with the cathode while the cathode is the last element formed and is formed after the remaining parts ci" the tube are in pov-sition and the tube is completely sealed except for the tip at the top of the bulb.

In accordance with the present invention the cathode and anode are formed outside of the bulb and mounted on the stem so that they can be inserted as a unit in the bulb by positioning the stem in place in the bulb. The stem is then fused into the bulb and thn only operation performed through the tip of the tube is the exhaustion of the bulb and the introduction or an inert gas under low pressure where such a gas is used.

An object of the invention is to provide an improved photoelectric tube.

A further object is to provide a photoelectric `tube of such a construction as to be simple to manufacture.

A further object is to provide a photoelectric tube or" a rugged construction in which the elecf trodes are mounted on the stein of the envelope Y @ther objects and advantages will appear as the description proceeds.

Another object is to make possible a uniform spacing and arrangement of electrodes.

Referring to the drawing- A Fig. 1 is a cross-sectional view of a tube embodying my invention;

Fig. 2 is a' detailed view of the stem and electrodes of the tube taken on line 2 2 of Fig. 1.

Fig. 3 is a horizontal section of the cathode of the device of Fig. 1;

Fig. 4 is a detail view of a modied form of cathode;

Fig. 5 is a sectional view taken on line 5- of Fig. 4; and Fig. 6 is a horizontal section through the cathode of Fig. 4.

In the preferred form of my invention I provide a bulb or envelope for enclosing the electrodes of the photoelectric tube. The lower porl tion of the bulb has a neck '7 into which the stem or press 8 is fused as is'well known in the art.

A cathode 9 and anode 11 are mounted directly on the stem so that the fusing of the stem into the bulb properly positions these elements within the tube. y

Cathode 9 comprises a thin plate 12 of a nonconducting material such as glass, which is clamped along opposite edges by two strips of U-shaped conducting material 13. The lower ends oi the strips are also clamped about conducting supports 14, one or both of which may pass through the stem to be connected to a prong i5 secured to base 16 of the tube.

The anode comprises a looped wire positioned in front of the cathode and also passing through the stem for connection to a prong 17, whereby the anode and cathode may be placed in an electrical circuit by making contact with these prongs. Only two prongs are required or a tube of the type described, although more may be provided for mechanical reasons and for supporting the tube in a standard socket.

After plate 12 has been mounted on the stem as described a layer oi an alkali-metal such as potassium is deposited thereon by placing the cathode in an atmosphere of volatized potassium and allowing the metal to condense thereon. When the plate is thus coated the coating will also extend over the strips 13 and thereby electrically interconnect the entire coating with the strips. In this manner an eicient and simple means is provided for placing the coating in an electrical circuit. When the plate has been coated with the alkali-metal it is placed in an atmosphere of hydrogen and the alkali-metal is converted into a hydride of the metal by a glow discharge between the cathode and the anode. The alkali-metal hydride is an eiicient and sensitive electron einissive medium which is responsive to emit electrons in accordance with the intensity of light impinging thereon. The process oi coating plate 12 and converting the surface into a hydride may be carried out in any suitable apparatus therefor.

The sensitized plate or cathode together with anode 11 are placed in the bulb with the stem 8, whereupon the stein is fused into the bulb. The bulb is then exhausted through tip 14 and an inert gas under low pressure may or may not be introduced. The tip is then sealed off, completing the tube.

In Figs. 4 to 5 a modified form of the invention is shown in which plate 12' is integrally supported on stem 8 by a pair of supports 14. Plate 12 is coated and sensitized in the same inanner as disclosed above, however, due to the fact that supports 14 are made of non-conducting material a conductor 21 is lead into the tube through the stem and resiliently engages the cathode, making electrical contact therewith. In some cases I also coat the plate with some other conducting material such as magnesium first which thus allows me to use a very thin layer of sensitive material and still have conductivity. It is important to have proper conductivity and this feature may be resorted to with beneficial results under some circumstances. Anode l1 as Well as the cathode is mounted on the stem and positioned with respectl thereto prior to inserting and fusing the stem into the bulb.

The tube of this invention has been found to be particularly well suited for usesin Whiclra.

large cathode area is not essentialv anddue to the simplicity of manufactureis an economical type of tube for certain applications of photoelectric tubes.

It will be understood that the embodiments of-theinvention illustrated` and described are merely convenient and practical forms of the invention and that many other modifications may be made Without departing from the spirit and scope of the invention.

What I claim as new and desire to protect by United States Letters Patent is:-

1. A photoelectric tube comprising an envelope, a stern extending into said envelope, a non-conducting plate, a pair of conducting strips supporting saidplate, an electron emissivesubstance forming a coating for said plate and making electrical conducting contact with said strips, a hydrile surface on said coating forming a light sensitive cathode, and an anode for receiving electrons therefrom.

2. Aphotoelectric tube comprising an envelope, a non-conducting plate, a pair of conducting strips clamping opposite edges of said plate for supporting the plate in said envelope, an alkalimetal coating on said plate contacting with said strips, one of said strips leading from said cell for connection in anelectrical circuitland an anode supported in .said envelope.`

ARCHIE J. MCMA'STER. 

